1. Working nature: triode is controlled by current, MOS tube belongs to voltage control.
2. Cost problem: triode is cheap, mos tube is expensive.
3. Power consumption problem: triode loss is large.
4. Drive capability: mos tube is often used for power switch and high current local switch circuit.
Transistor is cheaper, easy to use, commonly used in digital circuit switch control.
MOS tubes are used in high-frequency and high-speed circuits, high-current applications, and where the base or drain control current is more sensitive.
The MOS transistor can not only be used as a switching circuit, but also as an analog amplifier, because the change of the gate voltage within a certain range will cause the change of the on-resistance between the source and the drain.
The main difference between the two is that the bipolar tube is a current control device (a larger collector current is controlled by a smaller base current), and the MOS tube is a voltage control device (a gate voltage is used to control the on-resistance between the source and the drain).
Under the conduction voltage drop of MOS transistor (field effect transistor), the conduction resistance is small, the gate drive does not need current, the loss is small, the drive circuit is simple, the protection diode is provided, the thermal resistance characteristic is good, it is suitable for high-power parallel connection, and the disadvantage is that the switching speed is not high and it is relatively expensive.
The switching speed of the triode is high, the Ic of the large triode can be made very large, the disadvantage is large, the base drive current is large, and the drive is complicated.
Generally speaking, low-cost occasions, ordinary applications should first consider using triode, if not, consider MOS tube.
In fact, it is wrong to say that current control is slow and voltage control is fast. It takes a real understanding of how bipolar transistors and mos transistors work to understand. Triode works by the movement of carriers. Take npn tube emitter follower as an example. When no voltage is applied to the base, the pn junction composed of the base region and the emitter region prevents the diffusion movement of multiple sub (the base region is holes and the emitter region is electrons). At this pn junction, an electrostatic field (I .e. built-in electric field) from the emitter region to the base region will be induced. When the positive voltage applied to the base region points to the emitter region, when the electric field generated by the applied voltage of the base is greater than the built-in electric field, the carriers (electrons) in the base region may flow from the base region to the emission region. The minimum value of this voltage is the forward conduction voltage of the pn junction (generally considered as 0.7V in engineering). However, there will be charges on both sides of each pn junction at this time. If a positive voltage is applied to the collector-emitter, the electrons in the emission region will move to the base region under the action of an electric field (in fact, they all move in the opposite direction of electrons). As the width of the base region is very small, electrons can easily cross the base region to reach the collection region and recombine with the holes of PN here (close to the collector). In order to maintain balance, under the action of positive electric field, the electrons in the collector region accelerate the movement of the outer collector, while the holes move at the pn junction, which is similar to an avalanche process. The electrons in the collector return to the emitter through the power supply, which is how the transistor works. When the triode works, the two pn junctions will induce charges. When the switch tube is in a conduction state, the triode is in a saturated state. If the triode is closed at this time, the charges induced by the pn junction will return to a balanced state. This process takes time. The mos transistor works in a different way and does not have this recovery time, so it can be used as a high-speed switch tube.
(1) The field effect transistor is a voltage control element, and the transistor is a current control element. In the case of only allowing less current from the signal source, the field effect transistor should be selected; and in the case of low signal voltage and allowing more current from the signal source, the transistor should be selected.
(2) field effect transistor is the use of majority carrier conduction, so called a unipolar device, and the transistor is the majority of carriers, but also the use of minority carrier conduction. They are called bipolar devices.
(3) The source and drain of some field effect transistors can be used interchangeably, and the gate voltage can also be positive or negative, which is more flexible than transistors.
(4) FET can work under the condition of very small current and very low voltage, and its manufacturing process can easily integrate many FET on a silicon chip, so FET has been widely used in large scale integrated circuits.
(5) The field effect transistor has the advantages of high input impedance and low noise, so it is also widely used in various electronic devices. In particular, the use of field effect transistors as the input stage of the entire electronic device can obtain performance that is difficult to achieve in general transistors.
(6) FET is divided into two categories: junction type and insulated gate type, and its control principle is the same.
Other comparisons:
1. The triode is a bipolar tube, that is, when the tube works, the inside is participated by two carriers, hole and free electron.
Field effect tube is a unipolar tube, that is, the tube work either only holes, or only free electrons involved in conduction, only a carrier.
2. Transistor is a current control device, and only when there is an input current can there be an output current.
Field effect tube is a voltage control device, there is no input current will have output current.
3. The input impedance of the triode is small, and the input impedance of the FET is large.
4. Some FET sources and drains can be interchanged, and triode collectors and emitters cannot be interchanged.
5, the frequency characteristics of the field effect tube is not as good as the triode.
6. The noise figure of the field effect tube is small, which is suitable for the pre-stage of the low noise amplifier.
7. If you want the signal source current to be small, you should choose a field effect tube, otherwise it is more appropriate to choose a triode.